This invention relates to a calibration method and more particularly to a method for calibrating apparatus, such as a vector network analyzer, utilized for making evaluations of circuits operating at microwave and millimeter wave frequencies.
Most calibration methods used for electronic measurement apparatus require the use of a set of extremely high quality standards whose characteristics are known in advance. Additionally, a well known standard must be connected to verify the calibration procedure. Before any vector network analyzer system utilized for measuring the characteristic of devices can be used, it must be calibrated to remove any systematic errors in the measurement hardware. Accordingly, conventional calibration techniques at microwave or millimeter wave frequencies demand the fabrication of precise short circuits, open circuits and matched loads which need to be fabricated to exacting tolerances, not easily achieved. Moreover, such methods are inhibited by dispersion in the transmission medium, for example, microstrip, slotline, coplanar line, coplanar strips, etc. in which the measurement is performed. These dispersion characteristics are often unknown in millimeter wave integrated circuit devices thereby further compounding measurement difficulty. Also, the integrity of the operation hinges very critically on whether ideal electrical characteristics are reproduced at the launch plane for every calibration and verification device and for the device under test. Thus, conventional techniques do not furnish a convenient method for assessing the uncertainties due to variations in such characteristics.
A typical prior art calibration technique is disclosed in an article entitled, "Calibration of an Automatic Network Analyzer Using Transmission Lines of Unknown Characteristic Impedance, Loss and Dispersion", by E. F. daSilva et al. appearing in The Radio and Electronics Engineer, Vol. 48, No. 5, pp. 227-234, May, 1978.
It is an object of this invention, therefore, to provide an improved method for calibrating electronic measurement apparatus.
It is another object of this invention to provide an improved method for calibrating network analyzers for evaluating conventional and integrated circuits operating at microwave and millimeter wave frequencies.
It is still another object of this invention to provide an improved method for calibrating network analyzers by employing measurement redundancy to enhance stability, convergency, and accuracy of the measurements.
It is a further object of this invention to provide a method for calibrating vector network analyzers by utilizing relative characteristics among standards as opposed to their absolute characteristics.
It is yet a further object of this invention to provide a method for calibrating vector network analyzers which yields a direct and convenient measure of calibration quality.
It is still a further object of this invention to provide a self-verifying method for calibrating vector automatic network analyzers.